ASP.NET MVC Login ReturnUrl always NULL?

Question

Using Forms Authentication in ASP.NET MVC when trying to log back into a site, it puts a ReturnUrl parameter in the query string. My Logon action method accepts a "returnUrl" string. However it seems that returnUrl string is always null, even when it is clearly in the query string. Any thoughts on why this might be the case or a possible fix?

Answer 1

Maybe you don't include the ReturnURL parameter into you login form's action attribute, thus posting to a URL without that parameter?

Answer 2

Try the following:

        public static MvcForm BeginForm(this HtmlHelper htmlHelper, string id)
    {
        string formAction = htmlHelper.ViewContext.HttpContext.Request.RawUrl;

        TagBuilder tagBuilder = new TagBuilder("form");

        tagBuilder.MergeAttribute("id", id);
        tagBuilder.MergeAttribute("action", formAction);
        tagBuilder.MergeAttribute("method", HtmlHelper.GetFormMethodString(FormMethod.Post), true);

        HttpResponseBase httpResponse = htmlHelper.ViewContext.HttpContext.Response;
        httpResponse.Write(tagBuilder.ToString(TagRenderMode.StartTag));

        return new MvcForm(htmlHelper.ViewContext.HttpContext.Response);
    }

First ensure you have set the login url in the web.config, Next, ensure your Signin Form does not contain anything like action, for example:

View:

<%using (Html.BeginForm()){%> <%}%>

If you specify action you will always get null for return url:

Controller:

[AcceptVerbs(HttpVerbs.Post)] public ActionResult SignIn(string userName, string password, bool? rememberMe, string returnUrl) { }

Answer 3

This tends to happen when you're using one generic logon form, but you're explicitly specifying the Controller and ActionMethod (which is causing a form post, but losing the querystring)

Just to clarify, this is what your code should look like in your BeginForm:

Html.BeginForm("LogOn", "Account", new {ReturnUrl = Request.QueryString["ReturnUrl"] })

Answer 4

There are two ways I can think of to deal with logon and logoff scenarios. Dave Beer outlined one way, above. There is another approach that works in many situations. I used it when I coded the NerdDinner tutorial. The tutorial provides us with a logoff function that logs you off and takes you home. I did not want that. I wanted to return to the page I was on before I logged off. So I modified my Account controller logoff action to look like this

   public ActionResult LogOff()
    {
        FormsService.SignOut();
        return Redirect(Request.UrlReferrer.ToString());
    }

You can get fancier and pass in a returnUrl and test for it, in case you want to override this behavior. But I don't need that. This achieves the desired result. The Logon can work similarly. Maybe there are ways to use the MVC framework to do this for me, but until I learn them, this is VERY simple and works reliably.